The extent to which customary international laws of armed conflict protect the environment in non-international armed conflict has received very little critical attention to date when compared to the growing body of scholarship that examines the treaty-based environmental laws of international armed conflict. This article presents the first critical examination of the principles of distinction, proportionality, and the doctrine of military necessity and the extent to which they can be better interpreted to protect the environment during the conduct of hostilities in non-international armed conflict. In so doing, this article fills a key gap in understanding and knowledge and it moves the debate forward by suggesting ways in which the International Law Commission might develop more ambitious draft principles in their current programme of work.